The present invention relates to an organic glass copolymer for lens and a lens prepared therefrom. More particularly, the present invention relates to an excellent copolymer for lens having a high refractive index and the lens prepared therefrom.
In recent years organic glass lenses have come into wide use in place of inorganic glass lenses. Organic glass has characteristics which inorganic glass does not possess, namely advantages such as light weight property, higher safety, easier processability and good dyeability etc. Polymethylmethacrylate, polydiethyleneglycol bis-allylcarbonate, polycarbonate, polystyrene and the like have been widely utilized in various fields.
Especially in the field of the lens of ophthalmic glasses, light weight property and safety (impact resistance property) are strongly required. Therefore great hopes are entertained for organic glass having properties matched to those requirements. However, since a castable organic glass generally has a low refractive index (n.sub.D.sup.20 .apprxeq.1.50), organic glass has such defects that the lens composed thereof inevitably has a significantly great thickness compared to those of inorganic glass. On the one hand, organic glass having a relatively high refractive index, such as polycarbonate or polystyrene etc, cannot be processed by casting. Thus they are unsuitable for production of many kinds of articles, such as lens of ophthalmic glasses. The organic glass is actually restricted in their field of use to a certain narrow range because of their vulnerability to scratches in actual use caused by their low surface hardness, poor solvent resistance, low heat-resistance etc.
Various attempts have been made to heighten the refractive index of organic glasses.
For example polystyrene cannot be used as a material for lens because of their low surface hardness, inferior heat resistance, low solvent resistance, and low weatherability, and low dyeability, though it has a relatively high refractive index of 1.59. A method for improving surface hardness, weatherability of styrene by copolymerizing it with methylmethacrylate or acrylonitrile has already been known, but by this improvement, heat resistance and solvent resistance are hardly improved, though surface hardness and weatherability are improved in some degree, and further, the refractive index is gradually lowered in the improvement as the ratio of the second component in the copolymerization increases. Though the refractive indexes of the organic glass made of polyvinylnaphthalene, polyvinylcarbazol and polynaphthyl-methacrylate are relatively high, they have a high degree of self-coloring, and are very low in impact resistance and weatherability. Therefore these substances can never be used as a material for lens.
The inventors made an intense survey of various attempts to improve organic glasses. As a result of the survey on previous attempts to overcome the defects in the prior arts in the field of organic glasses, it has now been found that an organic glass having high refractive index, and having excellent surface hardness, solvent, head- and impact-resistance, good coatability, and the like can be obtained by copolymerizing a specific bifunctional acrylate or dimethacrylate with radically polymerizable monomer, homo-polymer thereof having a refractive index equal to or higher than 1.55.